1. Field of the Present Invention
This invention relates generally to a buffered fiber optic ribbon cable. In particular, the invention is directed to a fiber optic ribbon cable with a buffering layer to protect the fiber optic ribbon cable from the environment in which the fiber optic ribbon cable is installed.
2. Description of the Related Art
Installations of optical fiber as data transmission media for applications such as digital communications require increasingly diversified configurations of optical fiber cables. One such configuration of optical fiber cables is the optical fiber ribbon. An optical fiber ribbon is a type of flat cable that is simple to joint or xe2x80x9cconnectorizexe2x80x9d with, e.g., other optical fiber ribbons because mass jointing is easier than jointing independent cables. Further, because optical fiber ribbons reduce the need for manipulating individual optical fibers, optical fiber maintenance procedures are simplified.
Another benefit of optical fiber ribbons is the higher optical fiber density in the connecting plane. That is, more optical fibers can be connected along the plane of the optical fiber ribbon than can be connected using individual optical fibers. This is due to the tight formation of the optical fibers held in the ribbon matrix of the optical fiber ribbon.
Optical fiber ribbons typically consist of two or more parallel optical fibers held together by a ribbon matrix. The optical fibers are embedded in the ribbon matrix, which is typically a non-porous, insulative sheath made of ultraviolet (UV) curable resin or electron beam (EB) curable resin or the like. Each of the optical fibers embedded in the ribbon matrix generally comprises a coated glass core and cladding, etc.
FIG. 9 depicts a conventional optical fiber ribbon 2 in which a number (e.g., eight) of parallel optical fibers 4 are embedded in a ribbon matrix 6. A standard 8-fiber ribbon is shown, but this description applies to all ribbons of various fiber counts. Each of the optical fibers, which are held in place by the ribbon matrix, generally comprises a glass core 8, cladding 10, and outer coating 12 (which may comprise multiple coating layers). The ribbon matrix 6 surrounding the optical fibers 4 is typically made of a non-porous UV curable resin or the like which, when cured, partially molecularly bonds with the outer coating 12.
FIG. 10 shows a typical conventional installation situation in which several conventional optical fiber ribbons 2 are stacked on top one another and housed in a cable covering 14. The cable covering 14 is then filled with a filling gel 16 which further supports the optical fiber ribbons 2 stacked within the cable covering 14. Together, the conventional optical fiber ribbons 2, the cable covering 14 and the filling gel 16 comprise a fiber optic cable 18. The cable covering 14 provides protection from the environmental conditions of the surroundings in which the fiber optic cable 18 is installed.
The ribbon matrix of presently available optical fiber ribbons is not designed to protect the optical fibers it contains from harsh environmental conditions of the installation site. Rather, the typical UV curable ribbon matrix is partially molecularly bonded with the outer coating of the two or more parallel optical fibers in order to merely hold the optical fibers immediately adjacent to each other in a substantially planar ribbon-like manner. Since the ribbon matrix does not afford great protection for the optical fibers, the fiber optic ribbons are typically installed within a cable (i.e., housing or covering) which protects the fiber optic ribbons from various installation environment conditions. Often, a single outer protective cable will include numerous optical fiber ribbons, stacked one on another or otherwise disposed in the cable, and a filling gel or the like surrounding the numerous optical fiber ribbons within the cable. The installation of individual fiber optic ribbons without outer protective cable is neither known nor recommended.
It is known conventionally to provide a fiber optic microcable comprising a single optical waveguide encased in a buffer, which is then coated with a fiber reinforced protective sheath formed of UV light-cured resin (see, e.g., U.S. Pat. No. 5,636,307). This protective sheath consists of an UV light curable resin impregnated with fibers to enhance the physical strength characteristics of the microcable. Because the resin polymerizes almost instantaneously, there is no tendency for the resin to sag out of round as there is for microcable cured in a long oven. Therefore, the resulting microcable is uniformly round over its entire length. However, the microcable of ""307 is an individual optical fiber and therefore suffers from the same disadvantages when it comes to installation and jointing or xe2x80x9cconnectorizationxe2x80x9d (i.e., density in the connecting plane and the need to manipulate individual optical fibers), as compared to fiber optic ribbons.
It is also conventionally known to provide an optical fiber multi-ribbon comprising at least two individual initial optical fiber ribbons that are positioned side-by-side in a common plane and surrounded by a common exterior sheath (see, e.g., U.S. Pat. No. 5,905,835). Each of the individual initial optical fiber ribbons comprises an individual sheath for assembling the optical fibers of each ribbon together side-by-side and in a common plane. The individual sheaths of the individual initial optical fiber ribbons and the common exterior sheath are made from the same resin. However, the optical fiber multi-ribbon disclosed of ""835 is designed to be used in a high-density optical cable, wherein the optical fiber multi-ribbon is housed within an outer protective housing (the cable), which provides protection from the installation environment. In other words, the common exterior sheath disclosed in ""835 is not suitable for installation without an additional protective cable covering. Moreover, the common exterior sheath of the optical fiber multi-ribbon of ""835 merely bonds the individual initial optical fiber ribbons together. The common exterior sheath does not function to protect each individual initial optical fiber ribbon in the event the individual initial optical fiber ribbons are split apart. Furthermore, the optical fiber multi-ribbon of ""835 contains no strengthening members.
It is also conventionally known to provide a porous buffer material for optical transmission media, wherein the porous buffer material directly surrounds the light transmitting fiber core (see, e.g., U.S. Pat. No. 5,675,686). The disclosed porous buffer material is a closed-cell porous polymer material which have more mechanical compliance compared to full density polymers because they contain a significant amount of void space. The essential purpose of a porous buffer material that directly surrounds the light transmitting fiber core is to widely distribute mechanical loads in both a temporal and spacial sense. This is because glass fibers are susceptible to fracture when subjected to closely distributed temporal loads, i.e. impact loads.
The porous polymers of ""686 offer improved temporal load distribution by having a lower amount of material in the loaded area. Since there is less material available to absorb the load, the effective unit loading is higher. This higher loading means that the material undergoes more plastic (versus elastic) deformation. The plastic (versus elastic) deformation, caused by less material available to absorb the load, prevents the load from being rapidly transferred to the fiber. The spacial load distribution is accomplished in a similar manner. Because there is less material in the area of the load, the load must be distributed over a wider area. Therefore, the porous buffering material of ""686 provides a special type of protection to optical fiber systems different from the standard ribbon matrix, which is a non-porous, insulative sheath made of UV curable resin or the like.
Finally, notwithstanding the benefits of using optical fiber ribbons over individual optical fibers, several disadvantages are associated with the presently available optical fiber ribbons. The drawbacks of using the presently available optical fiber ribbons housed within the outer protective cable include, among other things, a typically large increase in size of the installed cable (at least because of the wasted space between the optical fiber ribbons and the outer protective cable), and the additional manufacturing or installation step of covering the optical fiber ribbons with the outer protective cable.
It is an object of the present invention to overcome the above-mentioned drawbacks, whereby an individual optical fiber ribbon can be installed without being housed in an outer protective cable, thereby reducing the overall diameter of the installed cable and increasing the available installation adaptability of the cable to be installed.
The above and other objects are achieved by a first aspect of the present invention in which a buffered optical fiber ribbon cable includes at least one optical fiber ribbon cable, comprising a plurality of parallel optical fibers encased in a ribbon matrix sheath, and a buffering layer surrounding the optical fiber ribbon cable. The ribbon matrix sheath is at least partially molecularly bonded to outer coatings of the optical fibers and surrounds the plurality of parallel optical fibers, thereby holding the plurality of optical fibers immediately adjacent one another. The ribbon buffering layer comprises a material that allows the buffered optical fiber ribbon cable to be installed in environments independent of any additional protective cable covering.
Further, the material of the ribbon buffering layer is preferably UV curable resin or thermoplastic material. Also, the ribbon buffering layer material may further contain imbedded reinforcement fibers for strengthening the buffering layer. Moreover, the buffered optical fiber ribbon cable may have an optional outer buffering layer, surrounding the ribbon buffering layer, for added protection from the environment (e.g., fire retardant properties).
Another aspect of the present invention relates to a buffered optical fiber ribbon cable as described above, however, the buffered optical fiber ribbon cable includes a plurality of individually buffered optical fiber ribbon cables surrounded by an outer packaging buffer. The outer packaging buffer may have ripcords for separating the outer packaging buffer in order to access and split apart the individually buffered optical fiber ribbon cables. The individually buffered optical fiber ribbon cables can then be installed and used independent from each other, because each has the ribbon buffering layer comprising a material that allows the individually buffered optical fiber ribbon cable to be installed in environments independent of any additional protective cable covering.
The embodiments hereinafter described allow the fiber optic ribbon cable to be installed independent of any additional protective cable covering, and allow the fiber optic ribbon cable to be installed as independent cables where considerably smaller cable size is optimal.
These and other features and advantages of the present invention will be evident from the following description of the preferred and other embodiments shown in the accompanying figures.